Social facilitation among adult Papilionoidea across the Himalayan foothills of West Bengal, India

Social facilitation highlights a phenomenon among individuals forming groups associated with behavioral changes that are induced due to the presence of other conspecific organisms. Such an event happens through group interactions between these individuals further increasing in frequency or intensity with time. Bibliographic research has revealed the presence of such activity among insect orders (Blattodea, Isoptera, and Hymenoptera). The present investigation attempted to explore such aggregation-stimulating behavior among Lepidoptera (Superfamily: Papilionoidea) across the Himalayan foothills of West Bengal, India. Specially designed transects (500-800 m) were laid across the study site for observation of the cluster formation among adult butterflies. The mean number of butterfly species was noted at each cluster to determine the Resource Preference Index (RPI). Wing wear was used to ascertain the age of the butterflies, as wings are not repaired with age. Hierarchical clustering was used to illustrate the similarity in the duration of the association of a species with its resource. The association of butterflies at mud puddles and pond edges, in damp soil, and on carrion, animal dung, and bird droppings was significant. The formation of such aggregations exclusively by Papilioninae (Family: Papilionidae), Coliadinae, and Pierinae (Family: Pieridae) is worth mentioning. Danainae (Family: Nymphalidae) practiced pharmacophagy (gathering pyrrolizidine alkaloids) by aggregating on dead, damaged, or withered plant species (Apocynaceae, Asteraceae, Boraginaceae, and Fabaceae). During puddling on non-floral resources, butterflies, i.e, Graphium, Chilasa, Papilio, Eurema, Catopsilia, Colotis, Ixias, and Appias, gather supplementary nutrients. Such activity is generally performed predominantly by younger males and rarely by older females. Euploea, Tirumala, and Danaus are known to engage in the repeated scratching of dried plant parts to gather pyrrolizidine alkaloids. Such alkaloids serve as male pheromones stimulating courtship. Thus, social facilitation among Papilionoidea occurs to enhance its resource acquisition and decrease predation risk through increased vigilance and dilution effects.